Telephone signaling system



April 15, 1930. E w. NILES ET AL 1,

TELEPHONE SIGNALING SYSTEM Filed Sept. 24. 1928 INVENTORS ATTORNEYPatented Apr. 15, 1930 UNITED STATES PATENT OFFICE ELIOT W. N ILES, OFBLOOMFIELD, NEW JERSEY, AND WILLIAM H. EDWARDS, OF BAY- SIDE, NEW YORK,ASSIGNORS TO AMERICAN TELEPHONE AND TELEGRAPH COM- IPANY, A CORPORATIONOF NEW YORK TELEPHONE SIGNALING SYSTEM Application filed September 24,1928. Serial No. 307,831.

This invention relates to telephone systems and more particularly toimprovements in the circuits utilized for signaling purposes on suchsystems.

When it is desired to signal or ring a telephone subscriber, thesubscribers line is connected at the central oflice with a circuitincluding a source of signaling current and a tripping relay. When thesubscriber answers, the tripping relay will operate and disconnect theringing or signaling source from the line. The tripping relay is usuallyin series with the ringing source and the ringing current will passthrough the trip ping relay but will not operate it as it is adjusted sothat it will not operate on this current. When the subscriber answersand takes his receiver off the hook, a lower impedance is presented tothe ringing current at the station, thereby permitting a larger amountof alternating current to flow through the tripping relay. In certaintypes of alternating current machine ringing systems, the tripping relaywill be adjusted so that it will operate on this increased amount ofcurrent, thereby stopping the application of ringing current to theline. On this type of ringing system, it is necessary that the trippingrelay be adjusted so that it will not operate falsely when ringing onshort loops having extension ringers. This necessitates marginaladjustment of the tripping relay on alternating currents, which limitsthe maximum loop and requires considerable maintenance.

Another type of ringing system heretofore utilized is the so-calledalternating current-direct current type. In this type of sys tem, thereis provided a battery in series with the usual alternating currentringing source. When ringing, before the subscriber answers, there is nodirect current path at the subscribers station as the usual condenser isin the ringer circuit. However, when the party answers and completes histransmitter circuit, apath for direct current is provided. This directcurrent operates the tripping relay which can be designed not to operateon alternating current alone. This type of system, however, has thedisadvantage that with the addition of the series direct currenttripping battery necessitates a reduction of the alternating currentvoltage, thus reducing the power available to operate the ringers at thestation witn a corresponding sacrifice in loop ringing range. 1 i

It is the object of the arrangements of this invention to improve thetripping of machine ringing, without introducingother disadvantages, sothat maintenance will be reduced and longer loops will be permissible. Afurther object is to improve tripping without affecting ringing. Otherobjects and features of the invention will appear more fully from thedetailed description thereof hereinafter given. i

The invention may be more fully understood from the followingdescription together with the accompanying drawing in the figure ofwhich is a circuit diagram illustrating a preferred embodiment of theinventlon.

In the drawing is shown a subscribers line 1 terminating in the j acl: 2at a central oifice. By means of a plug 8, connection may be establishedwith a circuit including a source 13 of alternating ringing current withthe marginal tripping relay l2 responsive to unidirectional current inseries therewith. At the subscribers station, there is shown the ringingapparatus 3 bridged across the circuit in series with the condenser 4.The receiver 5, transmitter 6 and switchhook 7, are also shown. Arectifier 40 preferably of the contact variety, such. for example, as acopper oxide rectifier, is included in the subscribers set in thetransmitter circuit. This rectifier is poled so that the direct currenttransmitter supply and the fluctuations imposed upon it by thetansmitter during talking will be unimpeded. Regular alternating ringingcurrent isused without the necessity ofa tripping battery in series withit. During the current passes freely through the circuit and thetripping relay. The other polarity of current is blocked by therectifier. Thus, pulsating direct current is made available to operatethe tripping relay. This permits of designing the tripping relayto'bevery sensitive to direct current and insensitive to alternatingcurrent. Accordingly, the arrangements of the invention will provide theadvantage oftripping over considerably longer subscribers loops thanheretofore.

A more detailed description ofothe operation of the arrangements is asfollowsz' When the plug 8 is inserted in jack 2, the following circuitis closed; from ground connected to sleeve of jack 2, winding of therelay connectedto sleeve of plug 8, to battery and ground. This'willoperate the sleeve relay of plug .8 and close the following circuit;from ground and contact of sleeve relay of plug 8, conductors and 21,contact of trippin relay 12, conductor 22, left hand contact of relay23, conductor 24, winding of relay 10 to battery 27 and ground. It ispointed out that when the above, traced circuit is completed, a shortcircuit is esta lished around the winding of relay 23 and it remainsunoperated at this time. The operation of relay 10 will connect ringingcurrent to the rin conductor of circuit 9 and thence over line 1 to thesubscribers set. Ringing current will be applied to the ring conductorof circuit 9 from the alternating current source 13, interrupter-14,winding of; relay 12, conductor 28, contact and armature of relay -10 tothe ring conductor of circuit9. Itis pointed out that this ringingcurrent will not operate relay 12 v at this time as it is a marginalrelay adjusted to operate on unidirectional current only. This ringingcurrent will operate the bell 3 at the subscribers set When thesubscriber answers in response to the bell 3a low res'istancepath iscompleted through therectifier 40. One polarity of the alternatingringing current passes freely through the circuit including rectifierand the tripping relay 12. The other polarity of current is blocked bythe rectier. Thus pulsating direct current will transverse the circuitincluding the marginal relay 12. As this relay will operate onunidirectional current, such as this pulsating current, it will nowoperate. 1 The operation of relay 12 will break at its armature andcontact the previously traced circuit for relay 10.' This willremove theshort circuit around relay 23. The circuit will then be completed asfollows: from ground and coners set with a central oflice, a source ofaltertact oif sle'e-ve relay of plug-8, conductor 20, windingof relay23, conductor'25, winding of relay 10, to battery 27 and ground. Thiswill operate relay 23 and-close the following circuit; from ground andbattery 26, right. hand contact of-relay 23, conductor 24, winding ofrelay 10, to battery 27 and ground. As like poles of both equalbatteries 26 and 27 are connected to this circuit, the relay 10 will bede-energized. This will cut off the ringing current from the line andcomplete the line for talking purposes.

In systems utilizing common battery signaling and local battery talkingstations, the rectifier could be placedin either side of the line sothat the ringing current through the ringer is not rectified, but theringing current through the secondary of the induction coil is rectifiedwhen the party answers.

With. harmonic ringing systems the alternating current-direct currentmethod has heretofore been used exclusively for tripping purposesinasmuch as it was not feasible-to design an alternating currenttripping relay with the required margins for each of the variousfrequencies employed. As a relatively high voltage is also requiredtooperate the ringers in this type of system, the restriction in looprange referred to above is especially severe. The arrangements of theinvention, accordingly, are especially advantageous for harmonic ringingsystems, due to the high eflective ringing and tripping voltages whichthey afford without exceeding a safe limit for the maximum instantaneousvoltage. V

While the invention has been disclosed as embodied in certain specificarrangements, which are deemed desirable, it is understood that it iscapable of embodiment in many other forms Without departing from thespirit of the invention as defined by the appended claims.

What is claimed is: I 1. A telephone line connecting a subscribers setwith a central oflice, a source of alternating ringing current at saidcentral office, a tripping relay in series with said source responsiveonly to unidirectional current, and rectifying means in the talkingcircuit of said subscribers set.-

2. A telephone line connecting a subscribers set with a central oifice,a source of alternating ringing current at saidcentral office, atripping relay in series with said source, said relay being responsiveonly tounidirec- ,tional current, means to connect saidsource of ringingcurrent to said line, an alternating current path bridged across saidline at said subscribers set, signal responsive means in said path,means responsive when said subscriber answers for completing said lineas a direct current circuit, and rectifying means in said line as socompleted.

3. A telephone line connecting a subscribsaid relay being responsiveonly to unidirectional current, means to, connect said, source ofringing current to said line, and means responsive when said subscriberanswers for rectifying the current transmitted from said source throughsaid relay.

4;. A telephone line connecting a subscribers set with a central oflice,a source of alternating ringing current at said central otfice, atripping relay in series with said source, said relay being responsiveonly to unidirectional current, and a rectifier of the contact varietyin series in said talking circuit at said subscribers set, saidrectifier allowing the transmission therethrough of talking currents.

5. A telephone line connecting a subscribers set with a central oflice,a source of alternating ringing current at said central olfice, atripping relay in series with said source, said relay being responsiveonly to unidirectional current, a source of direct current for signalingpurposes at said central oflice, and a rectifier of the contact varietyin series in said talking circuit at said subscribers set, saidrectifier being so poled as to allow the transmission therethrough ofcurrents from said direct current source used for signaling.

In testimony whereof, we have signed our names to this specificationthis 22nd day of September, 1928.

ELIOT W. NILES. WILLIAM H. EDWARDS.

